This invention relates to a fuel cell, and more particularly to a fuel cell of the type which uses hydrogen sulfide or hydrogen gas containing hydrogen sulfide as its fuel.
In most oil refineries, heavy oil and other similar fractions are desulfurized for the purpose of preventing environmental pollution. The desulfurizing process generates hydrogen sulfide. Also in the processes for gasification or liquefaction of coal, hydrogen sulfide occurs as a secondary product. The hydrogen sulfide which issues as a by-product in these processes must be disposed of. As methods of disposal, various wet oxidation processes have been proposed wherein a gas containing hydrogen sulfide is brought into contact with a liquid catalytic composition so as to convert the hydrogen sulfide into elementary sulfur (hereinafter referred to simply as "sulfur"). This process involves a reaction represented by the formula (1) shown below. ##EQU1##
This is an exothermic reaction (.DELTA.H=-63.5 Kcal/mol) comparable in magnitude of heat evolution to the combustion of hydrogen (.DELTA.H=-68.3 Kcal/mol). In the desulfurization of a large amount of crude oil, the thermal energy liberated by this exothermic reaction reaches a level too high to be negligible. A standard desulfurization system, for example possesses a capacity for treating about 60,000 barrels/day of heavy oil and by-produces about 200 tons/day of hydrogen sulfide. From a theoretical point of view it should be possible to advantageously utilize this by-produced hydrogen sulfide as the fuel for a fuel cell since the standard oxidation-reduction potentials of hydrogen sulfide and its ions (S.sup.2-) are +0.14 volt and -0.48 volt and they differ from the potential, +1.23 volt, of hydrogen invariably by more than 1 volt. When hydrogen sulfide is made to react on the gas electrode as in the ordinary fuel cell, however, the catalyst for the fuel cell is poisoned by hydrogen sulfide and the sulfur formed by the reaction of the aforementioned formula (1) is deposited on the negative electrode on the fuel side and inseparably retained there. In the fuel cell which uses, as the fuel therefor, a substance containing hydrogen sulfide even in a very small amount, therefore, it is imperative that special consideration should be paid to the negative electrode.